Trends in Mean Energy and Nutrient Intakes in Japanese Children and Adolescents: The National Health and Nutrition Survey, 1995–2019

This study aimed to describe the national trends in mean energy and nutrient intakes in Japanese children and adolescents from 1995 to 2019. We used data obtained from the National Health and Nutrition Survey and included 54,871 participants aged 1–19 years. The dietary intake was estimated using a 1-day, semi-weighed, household-based, dietary record. The trends of mean energy and nutrient intakes were analyzed using the Joinpoint Regression Program. A declining trend in the mean energy intake was observed in toddlers aged 1–6 years, school girls aged 7–14 years, and adolescent girls aged 15–19 years, while the mean energy intake from protein, fat, and carbohydrates changed little over time. The mean salt equivalent showed a decreasing trend in all age groups, although the 2019 mean values were above the tentative dietary goal for preventing lifestyle-related diseases, especially in adolescent boys. Declining trends in mean vitamin (vitamin A, vitamin B12, folate, vitamin D, and vitamin K) and mineral (calcium, iron, and copper) intakes were observed, while trends in the mean vitamin B6 and zinc intakes were unchanged since 2001. Continuous monitoring of dietary intake and further research are required to raise awareness of unhealthy diet habits and to improve the food environment for the healthy growth and development of children and adolescents.


Introduction
Dietary habits tend to change over time. Japanese adults have reported a decrease in total energy intake, energy intake from protein, and sodium intake, and an increase in energy intake from fat [1]. Moreover, higher-income groups have shown a trend toward a lower cereal intake in the past decade [2]. Children and adolescents who primarily share meals with their parents may also experience similar changes in dietary intake, but little is known about trends in nutrient intake in this age group. There is a high prevalence of stunted children younger than 5 years (7.1%, 2010) and a high percentage of underweight adolescents (19.8%, 2015) with increasing trends since the 1980s [3]. Therefore, assessing the intake status of essential nutrients for adequate child growth and development is important to determine countermeasures that will prevent child malnutrition.
In Japan, school lunches have been provided to children aged 6-14 years for approximately 70 years in accordance with the School Lunch Program Act. This act incorporates more than one third of the daily requirement for children with a moderate level of physical activity, as indicated in the Dietary Reference Intakes for Japanese (DRIs) [4,5]. Therefore, the nutrient intake of lunch meals in this age group should be stable. However, whether the daily intake, including other meals (breakfast and dinner), and the daily nutrient intake of preschool children and adolescents who do not receive school lunches, are adequate or insufficient over time remain unclear.

Statistical Analysis
The mean and standard deviation (SD) were calculated by sex, three age categories (1-6, 7-14, and 15-19 years), and the survey year. The trend analyses were performed using Stata Version 16.1 (StataCorp, College Station, TX, USA) and the Joinpoint Regression Program (Joinpoint Regression software, version 4.9.1.0; National Cancer Institute, Rockville, MD, USA) [12]. Joinpoint regression analysis uses statistical criteria to determine the minimum number of linear segments required to describe a trend and perform the annual percentage change (APC) for each segment. The Monte Carlo Permutation method was used to test if a change in the trend was statistically significant. Differences were considered statistically significant at p < 0.05.

Results
The trends in energy and nutrient intakes according to sex and age are shown in Table 1 (young boys aged 1-6 years), Table 2 (young girls aged 1-6 years), Table 3 (school boys aged 7-14 years), Table 4 (school girls aged 7-14 years), Table 5 (adolescent boys aged 15-19 years), and Table 6 (adolescent girls aged 15-19 years). The number of survey participants decreased over the years.

Discussion
This study showed the trends in energy and nutrient intakes in Japanese children and adolescents for 25 years. The overall trend was a decrease in energy and nutrient intakes, although some nutrient intakes remained unchanged or increased by sex and age group.
The number of survey participants has decreased over the years. This may be linked to the declining trend in the number of live births in Japan, ranging from 1,187,064 in 1995 to 865,239 in 2019 [13]. Moreover, the household response rates are relatively low (63.5%, 2019) [6], although the response rate of individual children and adolescents is unknown. For more detailed analysis of nutrient intake by age group, it would be necessary to increase the response rate of households with children and adolescents in future surveys.

Discussion
This study showed the trends in energy and nutrient intakes in Japanese children and adolescents for 25 years. The overall trend was a decrease in energy and nutrient intakes, although some nutrient intakes remained unchanged or increased by sex and age group.
The number of survey participants has decreased over the years. This may be linked to the declining trend in the number of live births in Japan, ranging from 1,187,064 in 1995 to 865,239 in 2019 [13]. Moreover, the household response rates are relatively low (63.5%, 2019) [6], although the response rate of individual children and adolescents is unknown. For more detailed analysis of nutrient intake by age group, it would be necessary to increase the response rate of households with children and adolescents in future surveys.
A declining trend in energy intake in boys (young group) and girls (all age groups) was observed in this study, which is consistent with adults [1], while the latest mean energy intake in 2019 was almost within the estimated energy requirement [10]. Moreover, we found that the mean energy intake from protein, fat, and carbohydrates changed little over time. The 2019 mean energy intakes were within the DG, except for the mean energy intake from fat in school and adolescent girls. A previous study showed that a higher household income was associated with higher energy from fat in adolescents [14]. This finding suggested that further study is required to determine the dietary fat source and the underlying factors that contribute to a high fat intake, especially in adolescents.
Although a decreasing trend in the mean salt equivalent in all age groups was observed in this study, the latest mean salt equivalent in 2019 was above the DG. Seasonings, such as soya sauce and soybean paste, account for approximately 70% of the dietary salt source [15]. Therefore, further salt-reduction measures need to be encouraged, especially in adolescent boys. These measures include expanding the options of low-sodium meals in school and university cafeterias, and by warning about salt consumption on food labels at on-campus stores.
Declining trends in mean vitamin A, vitamin B12, folate, and vitamin K intakes were observed, but none of the latest mean intakes in 2019 were deficient compared with the 2020 DRIs. However, the mean vitamin D intake decreased over time and was below the adequate intake, especially in adolescents. Because vitamin D deficiency can cause rickets and osteomalacia, high-risk adolescents may need to incorporate sunlight exposure and dietary modification with vitamin D supplements and vitamin D-fortified foods into their daily lives [16]. With regard to the decrease in vitamin A intake, it should be noted that prior to 2000, the International Unit (IU) was used as the unit of vitamin A intake.
A declining trend in the mean calcium intake was observed in all age groups, except for in school boys aged 7-14 years. Our finding that the mean calcium intake in young girls and adolescents was lower than the RDA is alarming. However, we observed trends in calcium intake from foods and did not consider calcium intake from breast milk or formula. Breast milk or formula may be able to compensate for this deficiency in calcium intake. Therefore, continued breastfeeding after the age of 1 year is recommended in Japan, in alignment with the World Health Organization's recommendation to continue breastfeeding until the age of 2 years and older [17]. Further research is required to assess the overall calcium intake, including breast milk and formula, especially for 1-2-year-olds.
A decreasing trend in the mean iron intake was found in all age groups, and the 2019 mean iron intake was within the RDA, except for that in young girls. The revisions to the Standard Tables of Food Composition in Japan (4th edition for the 1995-2000 survey and 5th edition for the 2001-2004 survey) may have affected the changes in iron intake since 2001. The World Health Organization warns that the global prevalence of anemia in children aged 6-59 months was 39.8% in 2019 [18], although the actual status of iron deficiency anemia in young Japanese girls is unclear. Therefore, more public health attention is required regarding iron intake and the risks associated with iron deficiency in young girls.
This study has several limitations. First, dietary intake assessed by self-administered dietary records might not represent long-term habitual intake. Second, certain groups may have underreported their dietary intake, because the underreporting of energy intake in young children (1-5 years) and adolescents (15-19 years) and in children with obesity has previously been reported [19]. Third, although three age categories are insufficient because of children's growth, nutrient intakes in the detailed age categories were unavailable in the survey reports from which the data were obtained. Fourth, while many nutrient intakes may have declining trends because the energy intake has decreased over the years, the survey reports do not disclose the values per 1000 kcal. Fifth, this study did not include nutrient intake from breast milk or formula in 1-2-year-olds. The National Nutrition Survey on Preschool Children showed that the percentage of children weaned by 12 months of age was 54.4% in 2005 and 34.7% in 2015 [20]. Sixth, children and adolescents with various illnesses requiring specific dietary regimens such as food allergies and diabetes could not be excluded from this study because the survey did not collect this information. Although these limitations should be noted when interpreting the results, this study showed the annual trends in mean energy and nutrient intakes using nationally representative data for Japanese children and adolescents over the last 25 years.

Conclusions
We found declining trends, with some exceptions, in energy and some nutrient intakes in Japanese children and adolescents from 1995 to 2019. Continuous monitoring of the dietary intake and further research are required to raise awareness of unhealthy diet habits and to improve the food environment for the healthy growth and development of children and adolescents.